2,3-Butanediol (which may hereinafter be referred to as “2,3-BDO”) is a useful compound used as an intermediate material for pharmaceuticals and cosmetics, and as a material for inks, perfumes, liquid crystals, insecticides, softening agents, explosives, plasticizers, and the like. More specifically, for example, 2,3-butanediol can be used as a material for methyl ethyl ketone (A. N. Bourns, The Catalytic Action of Aluminium Silicates, Canadian J. Res. (1947)) or 1,3-butadiene (Nathan Shlechter, Pyrolysis of 2,3-butylene Glycol Diacetate to Butadiene, Indu. Eng. Chem. 905 (1945)). Industrially, 2,3-BDO is produced by a method in which 2-butene oxide is hydrolyzed in an aqueous perchloric acid solution. In recent years, to solve the problems of depletion of petroleum resources and global warming, achievement of a sustainable, recycling-oriented society is demanded. Also in the chemical industry, shifting from petroleum materials to biomass-derived materials is being intensively studied. Under such circumstances, methods of producing 2,3-butanediol by microbial fermentation have begun attracting attention.
Known examples of microorganisms capable of efficiently producing 2,3-butanediol by fermentation include enterobacteria such as Klebsiella pneumoniae (Ma C Q, Enhanced 2,3-butanediol production by Klebsiella pneumoniae SDM, Appl Microbiol Biotechnol 2009; 82:49-57) and Klebsiella oxytoca (Ji X J, Engineering Klebsiella oxytoca for efficient 2,3-butanediol production through insertional inactivation of acetaldehyde dehydrogenase gene, Appl Microbiol Biotechnol 2010; 85:1751-8). Since these microorganisms do not require a particular vitamin, amino acid, or the like for the fermentation, their use is advantageous in that the processes required for isolation/purification of 2,3-butanediol from the fermentation liquid can be reduced. However, these microorganisms are pathogenic, and known to cause respiratory infections and the like. Therefore, when large-scale culture of these fermentation microorganisms is carried out for the purpose of industrial production of 2,3-butanediol, facilities for strict control are required, and the cost increases as a result.
There are disclosed methods using biologically safe 2,3-butanediol fermentation microorganisms showing high fermentation efficiency such as bacteria belonging to the family Bacillaceae including Bacillus licheniformis (S. S. Nilegaonkar, Potential of Bacillus licheniformis for the production of 2,3-butanediol, Journal of Fermentation and Bioengineering, Vol. 82, Issue 4, 1996, pages 408-410) and Bacillus amyloliquefaciens (Yang T, Optimization and scale-up of 2,3-butanediol production by Bacillus amyloliquefaciens B10-127, World J Microbiol Biotechnol, 2012 April; 28(4):1563-74). However, 2,3-butanediol fermentation by Bacillus licheniformis requires use of an animal extract, which is expensive, as a nutrient source for promoting the fermentation. 2,3-Butanediol fermentation by Bacillus amyloliquefaciens requires use of ammonium citrate for promotion of the fermentation. Since the boiling point of citric acid is close to that of 2,3-butanediol, isolation/purification of 2,3-butanediol is difficult when citric acid remains in the culture liquid.
On the other hand, as fermentation feedstocks for microbial fermentation, not only conventional sugars derived from edible biomass, but also sugars derived from non-edible biomass are attracting attention. When a sugar derived from non-edible biomass is used as the fermentation feedstock, cellulose, hemicellulose and the like contained in the non-edible biomass are decomposed into sugars using a saccharifying enzyme. In that process, pentoses such as xylose are obtained in addition to hexoses such as glucose. Therefore, development of an efficient fermentation technique for materials containing pentose has been demanded.
Known examples of microorganisms capable of efficiently producing 2,3-butanediol from pentose by fermentation include enterobacteria such as Klebsiella oxytoca (Ma C Q, Enhanced 2,3-butanediol . . . ). Since these microorganisms do not require a particular vitamin, amino acid or the like for the fermentation, their use is advantageous in that the processes required for purification of 2,3-butanediol from the fermentation liquid can be reduced. However, these microorganisms are pathogenic, and known to cause respiratory infections and the like. Therefore, when large-scale culture of these fermentation microorganisms is carried out for the purpose of industrial production of 2,3-butanediol, facilities for strict control are required, and the cost increases as a result.
On the other hand, there are disclosed methods using biologically safe microorganisms capable of producing 2,3-butanediol from pentose by fermentation such as bacteria belonging to the family Bacillaceae including Bacillus licheniformis (Wang Q, Metabolic engineering of thermophilic Bacillus licheniformis for chiral pure D-2,3-butanediol production, Biotechnol Bioeng, 2012 July: 109(7):1610-21) and Paenibacillus polymyxa (Marwoto B, Metabolic analysis of acetate accumulation during xylose consumption by Paenibacillus polymyxa, Appl Microbiol Biotechnol, 2004 March: 64(1):112-9). However, in 2,3-butanediol fermentation using these microorganisms, an expensive auxiliary material such as a yeast extract or animal protein hydrolysate needs to be used so that the cost is high.
There are known transformed microorganisms belonging to the genus Zymobacter and having a capacity to metabolize pentose, which microorganisms were prepared by introducing exogenous genes encoding xylose isomerase, xylulokinase, transaldolase, and transketolase into microorganisms belonging to the genus Zymobacter (JP 2005-261421 A, US 2007/0298476 A). However, although JP '421 and US '476 describe that the transformed microorganisms have a capacity to produce ethanol, there is neither description nor suggestion on a capacity to produce 2,3-butanediol from pentose by fermentation.
As described above, when a biologically safe microorganism is used in a conventional method of producing 2,3-butanediol by microbial fermentation, the cost is high, or separation from a by-product is difficult, which is problematic.
Accordingly, it could be helpful to provide a method of producing 2,3-butanediol by microbial fermentation utilizing a biologically safe microorganism and an economical method of producing 2,3-butanediol from a fermentation feedstock containing pentose as a carbon source, by microbial fermentation utilizing a biologically safe microorganism.